A wavelength selective switch (WSS) may be used in a test and measurement application of a light source signal, such as a laser source signal. In this type of application, the WSS may be used to create a channel around the light source signal. For instance, the WSS may apply an attenuation pattern on the light source signal to output a channel containing the attenuated light beam from the WSS. A testing station that is to implement the test and measurement application may be positioned to receive the attenuated light beam.